[cryout-pullquote align=”left” textalign=”left” width=”100%”](The following article was provided by Bob Maerdian for your reference. Referenced figures and illustrations are not available.)[/cryout-pullquote]
Sights & Shooting, Part II: CHANGING SIGHTS
© 1993 Tom Kelly
Last month, I discussed how sight picture changes will effect the bullet impact point (BIP) as a recommended alternative to whacking away at your sights. As much as I regret it, there are times when physical changes to the front and/or rear sight must be made, as a last resort. And, if you have never done refined sight work (like taking off 1/64th of an inch, or adding a blob of solder to the front sight to raise the front sight 3/64ths of an inch) you should seriously consider finding someone who has to assist you the first couple of times.
There is a protocol for considering sight construction/ destruction. First, you should have the absolute best group you can get out of the barrel PERIOD. Good sights don’t tighten a bad group. Furthermore, the purpose of altering sights is to realign the BIP based on the center of the group. Where is the center of a 10 inch group? There is far less error in computing the center of a 3 1/2 inch group then when the same computation is done on a 10 inch group. Second, you should try different sight pictures as discussed in last months column. One or two occasional bad performances with a load you know groups well may actually be weather-effected and can be corrected by sight picture adjustments on the line. Lastly, you must have a fair knowledge of your weapons physical characteristics and how much incremental changes in sights will affect BIP.
TYPES OF SIGHTS
There are three basic sight construction types I will discuss. The first, and most basic, is the Mississippi Rifle type. These consist of a “V” notched rear sight in a dovetailed barrel slot, and a front sight mounted directly on the barrel. This type of sight can be found on the Mississippi Rifle and the Murray Carbine reproductions.
Another sight construction type is the Enfield type. These consist of an elevation adjustable rear sight and a front sight combined with a bayonet mounting lug. The front sight is often replaced by a larger and wider “shooter” sight which does not allow the bayonet to be affixed to the barrel.
The final sight construction type I want to discuss is the rear leaf sight. These are standard on Springfield reproductions, and generally offer three rear sight elevations for the shooter. Front “shooter” sights will also be found on many modified barrels.
I have not and will not discuss PEEP SIGHTS. Peep sights are not generally allowed in competitions outside the N-SSA. In order to keep our discussions open to all competitive shooters, I will discuss open (notch) rear sights only. Peep sight owners may adapt the information in these articles to there situation. Photo A shows 3 front sights. From the left, they are the Navy Arms Enfield Musketoon, A Whitacre barrel with a replacement “shooter sight”, and a Dixie Gun Works 1861 Springfield barrel. Notice how much larger the replacement sight is — offering more possibilities to the sight worker. Photo B shows 3 rear sights. From the bottom, they are the Short Range Springfield Type, an original Enfield Long Range sight, and the Musketoon rear sight — notice the “Steps” on the
Enfield style rear sights.
Remember F.O.R.S. (FRONT OPPOSITE – REAR SAME). This mnemonic device helps us to recall that we want to move our front sight in the opposite direction of desired changes in BIP, while moving the rear sight in the same direction as desired changes in BIP.
APPROACHES TO SIGHT ALTERATIONS
My favorite sight type is the Enfield type. This style is also proper for those Springfield and Harper Ferry Models which include the “long-range” sight. The rear sight allows many different opportunities to change BIP without radically changing sights. Most sights of this type have four immediate levels of adjustment to consider in sight adjusting. The distances that each step, or bump, raises the rear sight notch differs tremendously from step to step and sight to sight, so each rear sight must be measured. To measure, use a good pair of dividers, and place the rear sight in the lowest position (no bump). Measure in 64ths of an inch the distance between the bottom of the rear sight notch and the top of the barrel. Now move the rear sight to the first bump, and measure again. Measure the second and third bump the same way. Create a table like the one below for your rear sight change increments.
As you can see from Table 1, this type of sight design has built-in rear sight changes. Use this capability. For example, if you want to raise your rear sight 1/16 of an inch to raise your BIP, it is easier to take a little off a bump then it is to reconstruct your rear sight notch. Using our example, if your first bump increment is 5/64th, you only need to take 1/64th off of the first bump and raise your rear sight to that bump. And, if that first bump is 3/64ths, you can add a blob of solder and sand it down until your increase is correct! Make sure you keep both sights of the sight even, to avoid twisting the rear sight.
Mississippi style sights are not as easy to change. As always, a good group is important. Rear sight adjustments are made by lightly tapping the rear sight in its’ slot in the direction you want to move it. Don’t forget F.O.R.S.! Front sight adjustments to Mississippi style sights are very difficult. Heating the sights by soldering on additional material may actually loosen the original sight. If your group is high (left or right), you can lower the rear sight notch appropriately. If your group is low, try buying a replacement rear sight with a very shallow or no notch at all. You can use the replacement sight to create a rear notch higher then the old one. If you can’t find a replacement sight, you can put some solder in the old sight notch and refile the notch.
Photo C demonstrates the great difference in sight radius between arms. The weapon on top is a custom-built reproduction of a Harpers Ferry Model 1855 Rifle Musket, with a 36 inch sight radius. The middle weapon is a custom-built Enfield Rifle, with a sight radius of 22 inches. The bottom weapon is a Navy Arms Musketoon, with a sight radius of 18 inches. Length of sight radius drastically effects sight work. To move a group 4 inches would take twice as much sight work on the Musketoon as it would on the Harpers Ferry!
TOOLS FOR SIGHT WORK
To physically change sights requires few tools and much patience. The tools in Photo E are all that is needed — a measuring tape with 32nds and/or 64ths marked, an accurate set of dividers, and a few small metal files.
In our example, lets imagine that our 2 1/2 inch group at 50 yards, fired from a benchrest, is centered 6 inches low and 3 inches left of the mark. Our sight radius is 30 inches, and our front replacement sight post is dovetailed, not soldered. Using the ratio-formula, we deduce that our vertical sight correction is 1/8 of an inch, and the horizontal sight correction is 1/16 of an inch (1500/30 = 50; 1 inch correction = 50 inches BIP movement downrange). Implementing the F.O.R.S. guidelines, we can either lower the front sight 1/8 of an inch (front opposite) or raise the rear sight the same amount (rear same). Likewise, we can move the front sight to the LEFT 1/16 of an inch, or move the rear sight 1/16th of an inch to the right. In our example, we would choose drifting the front sight 1/16th of an inch left, and removing 1/8th of an inch from the front sight.
Using your dividers or calipers, measure the height of your front sight and use you tape measure to determine exact height. See photo D. Reduce your dividers the required distance, 1/8th of an inch, and begin filing carefully on the top of the front sight, taking care to keep the sight top square. MEASURE FREQUENTLY. It is a good idea to shoot another group after you reduce the sight height. The sight is wider at the bottom, and you may find that the horizontal differential changes.
Next, using a center punch, nail set or drift, tap the front sight to the left 1/16th of an inch after scratching a reference mark on the barrel and sight base. When these marks are 1/16th of an inch apart, your sight has been corrected.
It is always a good idea to use some sort of front sight protector to guarantee they stay the way you want them. I like the great big ones, like in Photo F, because I lose the little brass ones. Whichever you get, use them! Hopefully, these past few articles have shown you one or two ways to get your groups hittin’ where you want – until the next time, shoot safe and have fun.